Th-POK regulates mammary gland lactation through mTOR-SREBP pathway

Super-enhancer profiling reveals ThPOK/ZBTB7B, a CD4+ cell lineage commitment factor, as a master regulator that restricts breast cancer cells to a luminal non-migratory phenotype

Despite efforts to understand breast cancer biology, metastatic disease remains a clinical challenge. Identifying suppressors of breast cancer progression and mechanisms of transition to more invasive phenotypes could provide game changing therapeutic opportunities. Transcriptional deregulation is central to all malignancies, highlighted by the extensive reprogramming of regulatory elements that underlie oncogenic programs. Among these, super-enhancers (SEs) stand out due to their enrichment in genes controlling cancer hallmarks. To reveal novel breast cancer dependencies, we integrated the analysis of the SE landscape with master regulator activity inference for a series of breast cancer cell lines. As a result, we identified T-helper-inducing Poxviruses and Zinc-finger (POZ)/Krüppel-like factor (ThPOK, ZBTB7B), a CD4+ cell lineage commitment factor, as a breast cancer master regulator that is recurrently associated with a SE. ThPOK expression is highest in luminal breast cancer but is significantly reduced in the basal subtype. Manipulation of ThPOK levels in cell lines shows that its repressive function restricts breast cancer cells to an epithelial phenotype by suppressing the expression of genes involved in the epithelial-mesenchymal transition (EMT), WNT/b-catenin target genes, and the pro-metastatic TGFb pathway. Our study reveals ThPOK as a master transcription factor that restricts the acquisition of metastatic features in breast cancer cells.

Leptin on the apical surface inhibits casein production and STAT5 phosphorylation in mammary epithelial cells

Leptin is a peptide hormone present in both the blood and milk. A close relationship between leptin and milk production in lactating mammary glands has been previously reported. However, how leptin influences milk production in lactating mammary glands remains unclear. Also, whether leptin in milk or blood influences mammary epithelial cells (MECs) during lactation needs further investigation. This study investigated the effects of leptin on mouse MECs using a culture model in which MECs produced milk components and formed less permeable tight junctions. Our results showed that β-casein production in MEC was inhibited by leptin in a concentration-dependent manner. Leptin also inactivated the signal transducer and activator of transcription 5 (STAT5), a transcription factor that facilitates milk production in MECs. Leptin treatment induced the activation of p38 and c-Jun N-terminal kinase (JNK) in MEC before STAT5 inactivation, and anisomycin, an activator of p38 and JNK, induced the inactivation of STAT5. Furthermore, leptin exposure on the apical surface of MECs inhibited β-casein production and inactivated STAT5. However, leptin exposure on the basolateral surface hardly caused these effects. These findings suggested that milk leptin, but not plasma leptin, inhibited milk production in MECs.

Super-enhancer profiling reveals ThPOK/ZBTB7B, a CD4 + cell lineage commitment factor, as a master regulator that restricts breast cancer cells to a luminal non-migratory phenotype

Despite efforts to understand breast cancer biology, metastatic disease remains a clinical challenge. Identifying suppressors of breast cancer progression and mechanisms of transition to more invasive phenotypes could provide game changing therapeutic opportunities. Transcriptional deregulation is central to all malignancies, highlighted by the extensive reprogramming of regulatory elements that underlie oncogenic programs. Among these, super-enhancers (SEs) stand out due to their enrichment in genes controlling cancer hallmarks. To reveal novel breast cancer dependencies, we integrated the analysis of the SE landscape with master regulator activity inference for a series of breast cancer cell lines. As a result, we identified T - h elper-inducing Poxviruses and Zinc-finger ( PO Z)/ K rüppel-like factor (ThPOK, ZBTB7B ), a CD4 + cell lineage commitment factor, as a breast cancer master regulator that is recurrently associated with a SE. ThPOK expression is highest in luminal breast cancer but is significantly reduced in the basal subtype. Manipulation of ThPOK levels in cell lines shows that its repressive function restricts breast cancer cells to an epithelial phenotype by suppressing the expression of genes involved in the epithelial-mesenchymal transition (EMT), WNT/β-catenin target genes, and the pro-metastatic TGFβ pathway. Our study reveals ThPOK as a master transcription factor that restricts the acquisition of metastatic features in breast cancer cells.

Codonopsis lanceolata polysaccharide ameliorates high-fat diet induced-postpartum hypogalactia via stimulating prolactin receptor-mediated Jak2/Stat5 signaling

This study aims to investigate the ameliorative effect of Codonopsis lanceolata polysaccharide (PCL) on mice with hypogalatia induced by a high-fat diet (HFD) and the potential underlying mechanism. We found that oral administration of PCL demonstrated significant benefits in countering the negative effects of HFD, including weight gain, hepatic steatosis, mesenteric adipocyte hypertrophy, and abnormal glucose/lipid metabolism. In addition, PCL improved mammary gland development and enhanced lactogenesis performance. Histologically, PCL ameliorated the retardation of ductal growth, reduced mammary fat pad thickness, improved the incomplete linear encapsulation of luminal epithelium and myoepithelium, and increased the proliferation of mammary epithelial cells. Flow cytometry analysis showed that PCL mitigated the detrimental effects of HFD on mammary gland development by promoting the proliferation and differentiation of mammary epithelial cells. Mechanistic studies revealed that PCL upregulated the levels of prolactin (PRL) and its receptor (PRLR) in the mammary gland, activated JAK2/STAT5 signaling pathway, and increased the expression of p63, ERBB4, and NRG1. Overall, PCL can ameliorate HFD-induced hypogalactia by activating PRLR-mediated JAK2/STAT5 signaling. Our findings offer a methodological and theoretical foundation for investigating the functional constituents of traditional Chinese medicine in the treatment of hypogalactia.

ZBTB7B is a permissive regulator of hepatocellular carcinoma initiation by repressing c-Jun expression and function

Hepatocarcinogenesis is a multi-step process. However, the regulators of hepatocellular carcinoma (HCC) initiation are understudied. Adult liver-specific gene expression was globally downregulated in HCC. We hypothesize that adult liver-specific genes, especially adult liver-enriched transcription factors may exert tumor-suppressive functions in HCC. In this study, we identify ZBTB7B, an adult liver-enriched transcription factor as a permissive regulator of HCC initiation. ZBTB7B is highly expressed in hepatocytes in adult livers, compared to fetal livers. To evaluate the functions of ZBTB7B in hepatocarcinogenesis, we performed hepatocyte-specific ZBTB7B knockout in hydrodynamic oncogene transfer-induced mouse liver cancer models. Hepatocyte-specific knockout of ZBTB7B promotes activated Akt and N-Ras-induced HCC development. Moreover, ZBTB7B deficiency sensitizes hepatocytes to a single oncogene Akt-induced oncogenic transformation and HCC initiation, which is otherwise incompetent in inducing HCC. ZBTB7B deficiency accelerates HCC initiation by down-regulating adult liver-specific gene expression and priming livers to a fetal-like state. The molecular mechanism underlying ZBTB7B functions in hepatocytes was investigated by integrated transcriptomic, phosphoproteomic, and chromatin immunoprecipitation-sequencing analyses. Integrative multi-omics analyses identify c-Jun as the core signaling node in ZBTB7B-deficient liver cancer initiation. c-Jun is a direct target of ZBTB7B essential to accelerated liver cancer initiation in ZBTB7B-deficient livers. Knockdown of c-Jun expression or dominant negative c-Jun expression delays HCC development in ZBTB7B-deficient livers. In addition, ZBTB7B competes with c-Jun for chromatin binding. Ectopic ZBTB7B expression attenuates the tumor-promoting functions of c-Jun. Expression of ZBTB7B signature, composed of 140 genes co-regulated by ZBTB7B and c-Jun, is significantly downregulated in early-stage HCCs compared to adjacent normal tissues, correlates to liver-specific gene expression, and is associated with good prognosis in human HCC. Thus, ZBTB7B functions as a permissive regulator of HCC initiation by directly regulating c-Jun expression and function.

Acylated Ghrelin Activates PI3K/mTOR Signaling Pathway by Promoting ThPOK Acetylation to Promote Milk Fat Synthesis in Bovine Mammary Epithelial Cells

Ghrelin regulates diverse physiological activities. However, the effects of this hormone on the milk fat synthesis remain unknown. This study aimed to investigate the effect of acylated ghrelin (AG) on milk fat synthesis by modifying the expression (knockdown or overexpression) of growth hormone secretagogue receptor 1a (GHSR1a) and Th-inducing POK (ThPOK) in primary bovine mammary epithelial cells (BMECs). The results showed that AG significantly increased the triglyceride relative content from 260.83 ± 9.87 to 541.67 ± 8.38 in BMECs via GHSR1a. ThPOK functions as a key regulatory target downstream of AG, activating the PI3K and mTOR signaling pathways to promote milk fat synthesis in BMECs. Moreover, AG-regulated ThPOK by increasing the EP300 activity, which promoted ThPOK acetylation to protect it from proteasomal degradation. In conclusion, AG increases ThPOK acetylation and stabilizes ThPOK through GHSR1a, thereby activating the PI3K/mTOR signaling pathway and ultimately promoting the milk fat synthesis in BMECs.

Effects of hydrostatic compression on milk production-related signaling pathways in mouse mammary epithelial cells

Mammary epithelial cells (MECs) secrete milk into the mammary alveolar lumen during lactation. The secreted milk accumulates in the alveolar lumen until milk ejection occurs, and excess milk accumulation downregulates milk production in alveolar MECs. Intramammary hydrostatic pressure also increases in the alveolar lumen in a manner dependent on milk accumulation. In this study, we investigated whether high hydrostatic compression directly affects lactating MECs, using a commercial compression device and a lactation culture model of MECs, which have milk production ability and less permeable tight junctions. High hydrostatic compression at 100 kPa for 8 h decreased β-casein and increased claudin-4 levels concurrently with inactivation of STAT5 and glucocorticoid receptor signaling pathways. In addition, high hydrostatic compression for 1 h inactivated STAT5 and activated p38 MAPK signaling. Furthermore, repeated rises and falls of the hourly hydrostatic compression induced activation of positive (Akt, mTOR) and negative (STAT3, NF-κB) signaling pathways for milk production concurrently with stimulation of casein and lactoferrin production in MECs. These results indicate that milk production-related signaling pathways in MECs change in response to hydrostatic compression. Hydrostatic compression of the alveolar lumen may directly regulate milk production in the alveolar MECs of lactating mammary glands.

Genetics, environmental stress, and amino acid supplementation affect lactational performance via mTOR signaling pathway in bovine mammary epithelial cells

Mammary glands are known for their ability to convert nutrients present in the blood into milk contents. In cows, milk synthesis and the proliferation of cow mammary epithelial cells (CMECs) are regulated by various factors, including nutrients such as amino acids and glucose, hormones, and environmental stress. Amino acids, in particular, play a crucial role in regulating cell proliferation and casein synthesis in mammalian epithelial cells, apart from being building blocks for protein synthesis. Studies have shown that environmental factors, particularly heat stress, can negatively impact milk production performance in dairy cattle. The mammalian target of rapamycin complex 1 (mTORC1) pathway is considered the primary signaling pathway involved in regulating cell proliferation and milk protein and fat synthesis in cow mammary epithelial cells in response to amino acids and heat stress. Given the significant role played by the mTORC signaling pathway in milk synthesis and cell proliferation, this article briefly discusses the main regulatory genes, the impact of amino acids and heat stress on milk production performance, and the regulation of mTORC signaling pathway in cow mammary epithelial cells.

Hepatic ZBTB22 promotes hyperglycemia and insulin resistance via PEPCK1-driven gluconeogenesis

Excessive gluconeogenesis can lead to hyperglycemia and diabetes through as yet incompletely understood mechanisms. Herein, we show that hepatic ZBTB22 expression is increased in both diabetic clinical samples and mice, being affected by nutritional status and hormones. Hepatic ZBTB22 overexpression increases the expression of gluconeogenic and lipogenic genes, heightening glucose output and lipids accumulation in mouse primary hepatocytes (MPHs), while ZBTB22 knockdown elicits opposite effects. Hepatic ZBTB22 overexpression induces glucose intolerance and insulin resistance, accompanied by moderate hepatosteatosis, while ZBTB22-deficient mice display improved energy expenditure, glucose tolerance, and insulin sensitivity, and reduced hepatic steatosis. Moreover, hepatic ZBTB22 knockout beneficially regulates gluconeogenic and lipogenic genes, thereby alleviating glucose intolerance, insulin resistance, and liver steatosis in db/db mice. ZBTB22 directly binds to the promoter region of PCK1 to enhance its expression and increase gluconeogenesis. PCK1 silencing markedly abolishes the effects of ZBTB22 overexpression on glucose and lipid metabolism in both MPHs and mice, along with the corresponding changes in gene expression. In conclusion, targeting hepatic ZBTB22/PEPCK1 provides a potential therapeutic approach for diabetes.

Freeze-dried powder of daylily bud improves bromocriptine-induced lactation disorder in rats via JAK2/STAT5 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Milk deficiency is a prevalent problem in the world. Daylily (Hemerocallis citrina Borani), called the Chinese mother flower, is a traditional vegetable and is believed to possess a galactagogue effect in China. Flavonoids and phenols are considered as the active ingredients of daylily to promote lactation and improve depression.

AIM OF THE STUDY

The aim of this study was to investigate the prolactin effects of freeze-dried powder of flower buds of H. citrina Baroni in rat and its action mechanisms.

MATERIALS AND METHODS

The chemical constituents of flower buds of H. citrina Baroni treated by different drying techniques were analyzed by ultrahigh pressure liquid chromatography-mass spectrometry. Sprague-Dawley (SD) rat model induced by bromocriptine was used to evaluate the effect of freeze-dried powder of daylily buds on promoting lactation. Network pharmacology method, ELISA, qPCR, and Western blot were used to clarify the action mechanisms.

RESULTS

We detected 657 compounds in daylily buds. The relative contents of total flavonoids and phenols in freeze-dried samples were higher than those in dried ones. Bromocriptine, as a dopamine receptor agonist, can significantly inhibit prolactin in rats. Daylily buds can restore the levels of prolactin, progesterone and estradiol depressed by bromocriptine, effectively improve the milk production of the rat, and promote the repair of rat mammary gland tissue. We analyzed the relationship between the chemical components of daylily buds and the genes related to lactation with network pharmacology method, revealing that flavonoids and phenols may be the active components that promoted milk production via JAK2/STAT5 pathway, which was confirmed by the results of qPCR and Western blot. Daylily buds can increase the mRNA expression of PRLR, CSN2, LALBA and FASN and the protein expression of PRLR, JAK2 and STAT5.

CONCLUSION

Daylily buds can improve the insufficient lactation of rats induced by bromocriptine through PRLR/JAK2/STAT5 pathway, and the freeze-dried processing method may better retain the active components of flavonoids and phenols that promote milk in daylily.

Dishevelled 2 regulates cancer cell proliferation and T cell mediated immunity in HER2-positive breast cancer

BACKGROUND

Dishevelled paralogs (DVL1, 2, 3) are key mediators of Wnt pathway playing a role in constitutive oncogenic signaling influencing the tumor microenvironment. While previous studies showed correlation of β-catenin with T cell gene expression, little is known about the role of DVL2 in modulating tumor immunity. This study aimed to uncover the novel interaction between DVL2 and HER2-positive (HER2+) breast cancer (BC) in regulating tumor immunity and disease progression.

METHODS

DVL2 loss of function studies were performed with or without a clinically approved HER2 inhibitor, Neratinib in two different HER2+ BC cell lines. We analyzed RNA (RT-qPCR) and protein (western blot) expression of classic Wnt markers and performed cell proliferation and cell cycle analyses by live cell imaging and flow cytometry, respectively. A pilot study in 24 HER2+ BC patients was performed to dissect the role of DVL2 in tumor immunity. Retrospective chart review on patient records and banked tissue histology were performed. Data were analyzed in SPSS (version 25) and GraphPad Prism (version 7) at a significance p < 0.05.

RESULTS

DVL2 regulates the transcription of immune modulatory genes involved in antigen presentation and T cell maintenance. DVL2 loss of function down regulated mRNA expression of Wnt target genes involved in cell proliferation, migration, invasion in HER2+ BC cell lines (±Neratinib). Similarly, live cell proliferation and cell cycle analyses reveal that DVL2 knockdown (±Neratinib) resulted in reduced proliferation, higher growth arrest (G1), limited mitosis (G2/M) compared to non-targeted control in one of the two cell lines used. Analyses on patient tissues who received neoadjuvant chemotherapy (n = 14) further demonstrate that higher DVL2 expression at baseline biopsy pose a significant negative correlation with % CD8α levels (r = - 0.67, p < 0.05) while have a positive correlation with NLR (r = 0.58, p < 0.05), where high NLR denotes worse cancer prognosis. These results from our pilot study reveal interesting roles of DVL2 proteins in regulating tumor immune microenvironment and clinical predictors of survival in HER2+ BC.

CONCLUSION

Our study demonstrates potential immune regulatory role of DVL2 proteins in HER2+ BC. More in-depth mechanistic studies of DVL paralogs and their influence on anti-tumor immunity may provide insight into DVLs as potential therapeutic targets benefiting BC patients.

Protocol for an observational study investigating hormones triggering the onset of sustained lactation: the INSIGHT study

INTRODUCTION

Lactation is a hormonally controlled process that promotes infant growth and neurodevelopment and reduces the long-term maternal risk of diabetes, cardiovascular disease and breast cancer. Hormones, such as prolactin and progesterone, mediate mammary development during pregnancy and are critical for initiating copious milk secretion within 24-72 hours post partum. However, the hormone concentrations mediating lactation onset are ill defined.

METHODS AND ANALYSIS

The primary objective of the investigating hormones triggering the onset of sustained lactation study is to establish reference intervals for the circulating hormone concentrations initiating postpartum milk secretion. The study will also assess how maternal factors such as parity, pregnancy comorbidities and complications during labour and delivery, which are known to delay lactation, may affect hormone concentrations. This single-centre observational study will recruit up to 1068 pregnant women over a 3-year period. A baseline blood sample will be obtained at 36 weeks' gestation. Participants will be monitored during postpartum days 1-4. Lactation onset will be reported using a validated breast fullness scale. Blood samples will be collected before and after a breastfeed on up to two occasions per day during postpartum days 1-4. Colostrum, milk and spot urine samples will be obtained on a single occasion. Serum hormone reference intervals will be calculated as mean±1.96 SD, with 90% CIs determined for the upper and lower reference limits. Differences in hormone values between healthy breastfeeding women and those at risk of delayed onset of lactation will be assessed by repeated measures two-way analysis of variance or a mixed linear model. Correlations between serum hormone concentrations and milk composition and volume will provide insights into the endocrine regulation of milk synthesis.

ETHICS AND DISSEMINATION

Approval for this study had been granted by the East of England-Cambridgeshire and Hertfordshire Research Ethics Committee (REC No. 20/EE/0172), by the Health Research Authority (HRA), and by the Oxford University Hospitals National Health Service Foundation Trust. The findings will be published in high-ranking journals and presented at national and international conferences.

TRIAL REGISTRATION NUMBER

ISRCTN12667795.

The adaptation of maternal energy metabolism to lactation and its underlying mechanisms

Maternal energy metabolism undergoes a singular adaptation during lactation that allows for the caloric enrichment of milk. Changes in the mammary gland, changes in the white adipose tissue, brown adipose tissue, liver, skeletal muscles and endocrine pancreas are pivotal for this adaptation. The present review details the landmark studies describing the enzymatic modulation and the endocrine signals behind these metabolic changes. We will also update this perspective with data from recent studies showing transcriptional and post-transcriptional mechanisms that mediate the adaptation of the maternal metabolism to lactation. The present text will also bring experimental and observational data that describe the long-term consequences that short periods of lactation impose to maternal metabolism.

NuRD complex recruitment to Thpok mediates CD4+ T cell lineage differentiation

Although BTB-zinc finger (BTB-ZF) transcription factors control the differentiation of multiple hematopoietic and immune lineages, how they function is poorly understood. The BTB-ZF factor Thpok controls intrathymic CD4⁺ T cell development and the expression of most CD4⁺ and CD8⁺ lineage genes. Here, we identify the nucleosome remodeling and deacetylase (NuRD) complex as a critical Thpok cofactor. Using mass spectrometry and coimmunoprecipitation in primary T cells, we show that Thpok binds NuRD components independently of DNA association. We locate three amino acid residues within the Thpok BTB domain that are required for both NuRD binding and Thpok functions. Conversely, a chimeric protein merging the NuRD component Mta2 to a BTB-less version of Thpok supports CD4⁺ T cell development, indicating that NuRD recruitment recapitulates the functions of the Thpok BTB domain. We found that NuRD mediates Thpok repression of CD8⁺ lineage genes, including the transcription factor Runx3, but is dispensable for Cd4 expression. We show that these functions cannot be performed by the BTB domain of the Thpok-related factor Bcl6, which fails to bind NuRD. Thus, cofactor binding critically contributes to the functional specificity of BTB-ZF factors, which control the differentiation of most hematopoietic subsets.

14-3-3β is essential for milk composition stimulated by Leu/IGF-1 via IGF1R signaling pathway in BMECs

The cell proliferation of bovine mammary epithelial cells (BMECs) and consequent milk synthesis are regulated by multiple factors. The purpose of this study was to examine the effect of 14-3-3β on cellular proliferation and milk fat/β-casein synthesis in BMECs and reveal its underlying mechanisms. In this study, we employed gene function analysis to explore the regulatory effect and molecular mechanisms of 14-3-3β on milk synthesis and proliferation in BMECs. We found that leucine and IGF-1 enhance cell proliferation and milk synthesis in a 14-3-3β-dependent manner and only exhibiting such effect in the presence of 14-3-3β. We further determined that 14-3-3β interacts with the IGF1R self-phosphorylation site and it additionally mediated leucine and IGF-1 to stimulate the synthesis of milk through the IGF1R-AKT-mTORC1 signaling pathway. In summary, our data indicated that 14-3-3β mediates the expression of milk fat and protein stimulated by leucine and IGF-1, leading to lactogenesis through IGF1R signaling pathway in BMECs.

Mammary epithelial cell transcriptome reveals potential roles of lncRNAs in regulating milk synthesis pathways in Jersey and Kashmiri cattle

Background

Long noncoding RNAs (lncRNAs) are now proven as essential regulatory elements, playing diverse roles in many biological processes including mammary gland development. However, little is known about their roles in the bovine lactation process.

Results

To identify and characterize the roles of lncRNAs in bovine lactation, high throughput RNA sequencing data from Jersey (high milk yield producer), and Kashmiri cattle (low milk yield producer) were utilized. Transcriptome data from three Kashmiri and three Jersey cattle throughout their lactation stages were utilized for differential expression analysis. At each stage (early, mid and late) three samples were taken from each breed. A total of 45 differentially expressed lncRNAs were identified between the three stages of lactation. The differentially expressed lncRNAs were found co-expressed with genes involved in the milk synthesis processes such as GPAM, LPL, and ABCG2 indicating their potential regulatory effects on milk quality genes. KEGG pathways analysis of potential cis and trans target genes of differentially expressed lncRNAs indicated that 27 and 48 pathways were significantly enriched between the three stages of lactation in Kashmiri and Jersey respectively, including mTOR signaling, PI3K-Akt signaling, and RAP1 signaling pathways. These pathways are known to play key roles in lactation biology and mammary gland development.

Conclusions

Expression profiles of lncRNAs across different lactation stages in Jersey and Kashmiri cattle provide a valuable resource for the study of the regulatory mechanisms involved in the lactation process as well as facilitate understanding of the role of lncRNAs in bovine lactation biology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08406-x.

Occludin is a target of Src kinase and promotes lipid secretion by binding to BTN1a1 and XOR

Lipid droplets (LDs) have increasingly been recognized as an essential organelle for eukaryotes. Although the biochemistry of lipid synthesis and degradation is well characterized, the regulation of LD dynamics, including its formation, maintenance, and secretion, is poorly understood. Here, we report that mice lacking Occludin (Ocln) show defective lipid metabolism. We show that LDs were larger than normal along its biogenesis and secretion pathway in Ocln null mammary cells. This defect in LD size control did not result from abnormal lipid synthesis or degradation; rather, it was because of secretion failure during the lactation stage. We found that OCLN was located on the LD membrane and was bound to essential regulators of lipid secretion, including BTN1a1 and XOR, in a C-terminus–dependent manner. Finally, OCLN was a phosphorylation target of Src kinase, whose loss causes lactation failure. Together, we demonstrate that Ocln is a downstream target of Src kinase and promotes LD secretion by binding to BTN1a1 and XOR.

Lipid droplets are an essential eukaryotic organelle, but how they are secreted has remained unclear. This study shows that the tight junction protein Occludin is a phosphorylation target of Src kinase; Occludin binds to BTN1A1 and XOR to facilitate lipid droplet secretion in mammary epithelial cells.

Exploration of the lactation function of protein phosphorylation sites in goat mammary tissues by phosphoproteome analysis

BACKGROUND

Protein phosphorylation plays an important role in lactation. Differentially modified phosphorylation sites and phosphorylated proteins between peak lactation (PL, 90 days postpartum) and late lactation (LL, 280 days postpartum) were investigated using an integrated approach, namely, liquid chromatography with tandem mass spectrometry (LC-MS/MS) and tandem mass tag (TMT) labeling, to determine the molecular changes in the mammary tissues during the different stages of goat lactation.

RESULTS

A total of 1,938 (1,111 upregulated, 827 downregulated) differentially modified phosphorylation sites of 1,172 proteins were identified (P values < 0.05 and fold change of phosphorylation ratios > 1.5). Multiple phosphorylation sites of FASN, ACACA, mTOR, PRKAA, IRS1, RPS6KB, EIF4EBP1, JUN, and TSC2 were different in PL compared with LL. In addition, the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the calcium signaling pathway, oxytocin signaling pathway and MAPK signaling pathway were enriched. The western blot results showed that the phosphorylation levels of ACACA (Ser80), EIF4EBP1 (Thr46) and IRS1 (Ser312) increased and JUN (Ser63) decreased in PL compared with LL. These results were consistent with the phosphoproteome results.

CONCLUSIONS

In this study, we identified for the first time the differentially modified phosphorylation sites in goat mammary tissues between PL and LL. These results indicate that the multiple differentially modified phosphorylation sites of FASN, ACACA, mTOR, PRKAA, IRS1, RPS6KB, EIF4EBP1, TSC2, and JUN and proteins involved in the calcium signaling pathway, oxytocin signaling pathway, and MAPK signaling pathway are worthy of further exploration.

Dynamically remodeled hepatic extracellular matrix predicts prognosis of early-stage cirrhosis

Liver cirrhosis remains major health problem. Despite the progress in diagnosis of asymptomatic early-stage cirrhosis, prognostic biomarkers are needed to identify cirrhotic patients at high risk developing advanced stage disease. Liver cirrhosis is the result of deregulated wound healing and is featured by aberrant extracellular matrix (ECM) remodeling. However, it is not comprehensively understood how ECM is dynamically remodeled in the progressive development of liver cirrhosis. It is yet unknown whether ECM signature is of predictive value in determining prognosis of early-stage liver cirrhosis. In this study, we systematically analyzed proteomics of decellularized hepatic matrix and identified four unique clusters of ECM proteins at tissue damage/inflammation, transitional ECM remodeling or fibrogenesis stage in carbon tetrachloride-induced liver fibrosis. In particular, basement membrane (BM) was heavily deposited at the fibrogenesis stage. BM component minor type IV collagen α5 chain expression was increased in activated hepatic stellate cells. Knockout of minor type IV collagen α5 chain ameliorated liver fibrosis by hampering hepatic stellate cell activation and promoting hepatocyte proliferation. ECM signatures were differentially enriched in the biopsies of good and poor prognosis early-stage liver cirrhosis patients. Clusters of ECM proteins responsible for homeostatic remodeling and tissue fibrogenesis, as well as basement membrane signature were significantly associated with disease progression and patient survival. In particular, a 14-gene signature consisting of basement membrane proteins is potent in predicting disease progression and patient survival. Thus, the ECM signatures are potential prognostic biomarkers to identify cirrhotic patients at high risk developing advanced stage disease.

MIEF2 reprograms lipid metabolism to drive progression of ovarian cancer through ROS/AKT/mTOR signaling pathway

MIEF2 (mitochondrial elongation factor 2) is one of the key regulators of mitochondrial fission. Bioinformatics analysis indicated that high expression of MIEF2 predicted a poor prognosis in ovarian cancer patients. However, the relationship between MIEF2 and aberrant lipid metabolism in OC remains elusive. In this study, we demonstrated that MIEF2 significantly promoted lipid synthesis, while has no significant effect on fatty acid uptake and oxidation in OC cells. MIEF2 enhanced de novo fatty acid synthesis through up-regulating the expression of sterol regulatory element binding protein 1 (SREBP1) and its transcriptional target lipogenic genes ACC1, FASN and SCD1. Meanwhile, MIEF2-promoted cholesterol biosynthesis through up-regulating the expression of sterol regulatory element binding protein 2 (SREBP2) and its transcriptional target cholesterol biosynthesis genes HMGCS1 and HMGCR. Mechanistically, increased mitochondrial reactive oxygen species (ROS) production and subsequently activation of AKT/mTOR signaling pathway was found to be involved in the up-regulation of SREBP1 and SREBP2 in OC cells. Moreover, cell growth and metastasis assays indicated that MIEF2-regulated fatty acid synthesis and cholesterol biosynthesis played a critical role in the progression of OC. Taken together, our findings indicate that MIEF2 is a critical regulator of lipid synthesis in OC, which provides a strong line of evidence for this molecule to serve as a drug target in the treatment of this malignancy.

A common genetic variant in zinc transporter ZnT2 (Thr288Ser) is present in women with low milk volume and alters lysosome function and cell energetics

Suboptimal lactation is a common, yet underappreciated cause for early cessation of breastfeeding. Molecular regulation of mammary gland function is critical to the process lactation; however, physiological factors underlying insufficient milk production are poorly understood. The zinc (Zn) transporter ZnT2 is critical for regulation of mammary gland development and maturation during puberty, lactation, and postlactation gland remodeling. Numerous genetic variants in the gene encoding ZnT2 (SLC30A2) are associated with low milk Zn concentration and result in severe Zn deficiency in exclusively breastfed infants. However, the functional impacts of genetic variation in ZnT2 on key mammary epithelial cell functions have not yet been systematically explored at the cellular level. Here we determined a common mutation in SLC30A2/ZnT2 substituting serine for threonine at amino acid 288 (Thr288Ser) was found in 20% of women producing low milk volume (n = 2/10) but was not identified in women producing normal volume. Exploration of cellular consequences in vitro using phosphomimetics showed the serine substitution promoted preferential phosphorylation of ZnT2, driving localization to the lysosome and increasing lysosome biogenesis and acidification. While the substitution did not initiate lysosome-mediated cell death, cellular ATP levels were significantly reduced. Our findings demonstrate the Thr288Ser mutation in SLC30A2/ZnT2 impairs critical functions of mammary epithelial cells and suggest a role for genetic variation in the regulation of milk production and lactation performance.

Occludin protects secretory cells from ER stress by facilitating SNARE-dependent apical protein exocytosis

Tight junctions (TJs) are fundamental features of both epithelium and endothelium and are indispensable for vertebrate organ formation and homeostasis. However, mice lacking Occludin (Ocln) develop relatively normally to term. Here we show that Ocln is essential for mammary gland physiology, as mutant mice fail to produce milk. Surprisingly, Ocln null mammary glands showed intact TJ function and normal epithelial morphogenesis, cell differentiation, and tissue polarity, suggesting that Ocln is not required for these processes. Using single-cell transcriptomics, we identified milk-producing cells (MPCs) and found they were progressively more prone to endoplasmic reticulum (ER) stress as protein production increased exponentially during late pregnancy and lactation. Importantly, Ocln loss in MPCs resulted in greatly heightened ER stress; this in turn led to increased apoptosis and acute shutdown of protein expression, ultimately leading to lactation failure in the mutant mice. We show that the increased ER stress was caused by a secretory failure of milk proteins in Ocln null cells. Consistent with an essential role in protein secretion, Occludin was seen to reside on secretory vesicles and to be bound to SNARE proteins. Taken together, our results demonstrate that Ocln protects MPCs from ER stress by facilitating SNARE-dependent protein secretion and raise the possibility that other TJ components may participate in functions similar to Ocln.

Interactome of vertebrate GAF/ThPOK reveals its diverse functions in gene regulation and DNA repair

GAGA associated factor (GAF) is a sequence-specific DNA binding transcription factor that is evolutionarily conserved from flies to humans. Emerging evidence shows a context-dependent function of vertebrate GAF (vGAF, a.k.a. ThPOK) in multiple processes like gene activation, repression, and enhancer-blocking. We hypothesize that context-dependent interaction of vGAF with a diverse set of proteins forms the basis for the multifunctional nature of vGAF. To this end, we deciphered the protein-protein interactome of vGAF and show that vGAF interacts with chromatin remodelers, RNA metabolic machinery, transcriptional activators/ repressors, and components of DNA repair machinery. We further validated the biological significance of our protein-protein interaction data with functional studies and established a novel role of vGAF in DNA repair and cell-survival after UV-induced DNA damage. One of the major risk factors for skin cutaneous melanoma is prolonged exposure of UV and subsequent DNA damage. vGAF is highly expressed in normal skin tissue. Interestingly, our analysis of high-throughput RNA-sequencing data shows that vGAF is heavily downregulated across all major stages of skin cutaneous melanoma suggesting its potential as a diagnostic biomarker. Taken together, our study provides a plausible explanation for the diverse gene regulatory functions of vGAF and unravels its novel role in DNA repair.

Lysine Enhances the Stimulation of Fatty Acids on Milk Fat Synthesis via the GPRC6A-PI3K-FABP5 Signaling in Bovine Mammary Epithelial Cells

Amino acids can enhance milk fat synthesis in bovine mammary epithelial cells (BMECs), but the molecular mechanism is not well-known. In this study, we explored the regulatory role and molecular mechanism of lysine (Lys) on milk fat synthesis induced by fatty acids (FAs). We show that Lys dose-dependently affects number of cells and milk fat synthesis, and has more stimulatory effects in the presence of FAs. Lys enhances FA-induced sterol regulatory element binding protein 1c (SREBP-1c) expression and maturation in a fatty-acid-binding protein 5 (FABP5)-dependent manner. We further show that the Lys stimulates FABP5 expression via the GPRC6A (GPCR, class C, group 6, subtype A)-PI3K (phosphatidylinositol 3-kinase) signaling. Lys dose-dependently affects GPRC6A expression and localization at the plasma membrane. In summary, our data reveals that Lys enhances FAs-stimulated SREBP-1c expression and maturation leading to milk fat synthesis via the GPRC6A-PI3K-FABP5 signaling in BMECs.

Chi-miR-3031 regulates beta-casein via the PI3K/AKT-mTOR signaling pathway in goat mammary epithelial cells (GMECs)

BACKGROUND

MicroRNAs can regulate gene expression at the posttranscriptional level through translational repression or target degradation. Our previous investigations examined the differential expression levels of chi-miR-3031 in caprine mammary gland tissues in colostrum and common milk stages.

RESULTS

The present study detected the role of chi-miR-3031 in the lactation mechanisms of GMECs. High-throughput sequencing was used to analyze transcriptomic landscapes of GMECs transfected with chi-miR-3031 mimics (MC) and a mimic negative control (NC). In the MC and NC groups, we acquired 39,793,503 and 36,531,517 uniquely mapped reads, respectively, accounting for 85.85 and 81.66% of total reads. In the MC group, 180 differentially expressed unigenes were downregulated, whereas 157 unigenes were upregulated. KEGG pathway analyses showed that the prolactin, TNF and ErbB signaling pathways, including TGFα, PIK3R3, IGF2, ELF5, IGFBP5 and LHβ genes, played important roles in mammary development and milk secretion. Results from transcriptome sequencing, real-time PCR and western blotting showed that chi-miR-3031 suppressed the expression of IGFBP5 mRNA and protein. The expression levels of β-casein significantly increased in the MC and siRNA-IGFBP5 groups. We observed that the down-regulation of IGFBP5 activated mTOR at the Ser2448 site in GMECs transfected with MC and siRNA-IGFBP5. Previous findings and our results showed that chi-miR-3031 activated the PI3K-AKT-mTOR pathway and increased β-casein expression by down-regulating IGFBP5.

CONCLUSIONS

These findings will afford valuable information for improving milk quality and contribute the development of potential methods for amending lactation performance.

FSP1-positive fibroblasts are adipogenic niche and regulate adipose homeostasis

Adipocyte progenitors reside in the stromal vascular fraction (SVF) of adipose tissues that are composed of fibroblasts, immune cells, and endothelial cells. It remains to be elucidated how the SVF regulates adipocyte progenitor fate determination and adipose homeostasis. Here, we report that fibroblast-specific protein-1 (FSP1)⁺ fibroblasts in the SVF are essential to adipose homeostasis. FSP1⁺ fibroblasts, devoid of adipogenic potential, are adjacent to the preadipocytes in the SVF. Ablation of FSP1⁺ fibroblasts in mice severely diminishes fat content of adipose depots. Activation of canonical Wnt signaling in the FSP1⁺ fibroblasts results in gradual loss of adipose tissues and resistance to diet-induced obesity. Alterations in the FSP1⁺ fibroblasts reduce platelet-derived growth factor (PDGF)-BB signaling and result in the loss of preadipocytes. Reduced PDGF-BB signaling, meanwhile, impairs the adipogenic differentiation capability of preadipocytes by regulating matrix metalloproteinase (MMP) expression, extracellular matrix remodeling, and the activation of Yes-associated protein (YAP) signaling. Thus, FSP1⁺ fibroblasts are an important niche essential to the maintenance of the preadipocyte pool and its adipogenic potential in adipose homeostasis.

White adipose tissue (WAT), which consists mostly of adipocytes, is not only a passive energy storage but also an active metabolic and endocrine organ in the body. The importance of maintaining proper adipose mass is emphasized by the fact that both adipose tissue excess—in obese individuals—and deficiency have adverse metabolic consequences. In order to maintain the number of adipocytes, there is a continuous turnover from preadipocytes in adults. Like any other adult stem cells and progenitor cells, cell fate and differentiation capability of preadipocytes are tightly regulated by a highly specialized niche. However, what constitutes the preadipocyte niche, and how the niche regulates preadipocyte function and adipose homeostasis, remain poorly known. In this study, we have identified fibroblast-specific protein-1 (FSP1)⁺ fibroblasts in the WAT stromal vascular fraction (SVF) of mice as the niche for preadipocytes. We show that FSP1⁺ fibroblasts with aberrant Wnt signaling fail to maintain the preadipocyte pool and its differentiation potential, resulting in loss of adipose tissue. We conclude that FSP1⁺ fibroblasts are a niche for preadipocytes and regulate adipose tissue homeostasis in adult mice.